It's as true of music as the original saying is of books: never judge an album by its cover. And yet when it comes to the music of sisters Sierra and Bianca Casady, AKA CocoRosie, it's becoming increasingly hard not to. While their 2004 debut La maison de mon rêve was accompanied by a fairly harmless watercolour of a rainbow, its follow-up, 2005's Noah Ark, featured a crudely drawn picture of three unicorns indulging in some sort of pornographic daisy chain while one vomits. For the The Adventures of Ghosthorse and Stillborn the pair sported moustaches, while their last album, 2010's Grey Oceans, was represented by possibly one of the worst album covers of all time – the pair of them wearing felt beards, blue felt hats with green hair and looking like two extras from Lord of the Rings if it were being staged by a primary school.

Still, if you can get past the whimsy and the penchant for kooky, there's a lot to love about the songs the pair conjure up, and Gravediggress – the first track to emerge from their forthcoming fifth album, Tales of a Grass Widow, and premiered here – is a definite highlight. Once again they manage to channel their love for the organic and the electronic into something that feels fresh and otherworldly, as the song slips from its medieval pump organ intro into an almost Timbaland-esque beat, built around the beatboxing skills of their producer, Tez. Thematically, the song is an imagined conversation between an abandoned child and an outcast old woman (the titular Gravediggress), with Bianca taking on the role of the child and Sierra using her croaky croon to play the older woman. It's refreshing to return the world of CocoRosie even for just one song.